In the exposure of a fine pattern of a semiconductor integrated circuit or the exposure of a drive circuit pattern in a large vision field of a display device as represented by a TFT (Thin Film Transistor) liquid crystal television or the like, it is necessary to expose a pattern faithfully to the original image with a small line width variation over the whole surface in the exposure area. Especially in the field of the semiconductor integrated circuit, a pattern with a line width of 0.5 .mu.m or less will be required to be exposed over the whole surface of a region of approximately 15 mm in the future. With the increase in the fineness of the pattern, however, the range of forming an image (depth of focus) will become .+-.1 .mu.m or less. For this reason, it is essential that the photoresist surface on a wafer accurately coincides with the surface where a pattern image is to be formed. In order to realize this, it is necessary to detect the inclination and height of the wafer surface (photoresist surface) in the exposure area accurately.
In a first well-known example disclosed in JP-A-63-7626, a laser diode beam is converged from a diagonal direction on the wafer surface and the height is detected by detecting the position of convergence. Also, according to this well-known example, the multiple reflection accompanying a multilayered structure of a wafer is handled by use of a three-wavelength semiconductor laser with the convergence point changed along the direction perpendicular to the diagonal incident direction thereby to determine heights of different places on the wafer. This well-known example, which is primarily intended to detect the height, is capable of detecting an inclination by taking measurements at positions changed along the direction perpendicular to the diagonal incident direction. An accurate value of an inclination is difficult to obtain, however, even if two positions are measured in a narrow area of about 20 mm in diameter. If the height detection of high accuracy is to be realized in this well-known example, it is necessary to attain sufficient convergence on the wafer, that is to say, to reduce the diameter of convergence as far as possible. The reduction in the diameter of convergence, however, requires an increased convergence angle of the convergence beam (the angle formed by the outermost beam of the convergence light fluxes to the main light beam), with the result that the incident angle of the principal ray would be unavoidably reduced. This reduction in angle (which reduces the angle from a line perpendicular to the wafer surface) increases the effect of the multiple interference due to the multilayered structure of the wafer for the reason mentioned below. This well-known example uses three wavelengths to cope with the problem. Since each wavelength is affected by the interference, however, the problem has yet to be basically solved.
According to a second well-known example disclosed in JP-A-63-199420 as a conventional method of inclination detection, on the other hand, a light beam for inclination detection having a different wavelength from the exposure wavelength is irradiated through a projection lens, the reflected light beam is converged and the inclination is detected from the convergence position. Since the light beam is applied to the wafer in a substantially perpendicular direction or at a small incident angle, however, the effect of interference with the light beam reflected from the base is not negligible, thereby making accurate detection difficult for the reason mentioned below.
Further, in a third well-known example disclosed in JP-A-63-247741 as a conventional method of detecting the height for a multilayered structure, the light beams reflected from the base film are separated. Such a method, however, is difficult to put into practice on a thin film used for the process of producing a semiconductor circuit.
The above-mentioned prior art fails to take into consideration that the information on the inclination and height in an exposure area is to be accurately obtained for a multilayered structure such as a wafer having a semiconductor circuit pattern, and therefore poses a problem in controlling the inclination and height with high accuracy as would be required for the future circuit pattern exposure of 0.5 .mu.m or less.
Also, conventional apparatuses for detecting the inclination of an optical multilayered structure such as a semiconductor wafer are such that, as described in JP-A-61-170605 providing the first well-known example, for instance, the light beam emitted from a laser diode 2002 in FIG. 28 is converted into a directive beam by a lens 2014 and is irradiated on a wafer 2004 from above, and the position of the reflected light is detected by a two-dimensional position detector 2020.
Also, an instrument for measuring the distance (height) and inclination of a general object of measurement including but not limited to an optical multilayered structure is disclosed in JP-A-62-218802 of FIG. 29 providing the second well-known example. In this well-known example, the inclination is determined by a second photo-detector for the light beam entering in perpendicular direction as in the first well-known example, and the distance (in the direction perpendicular to the surface of the object 2106 to be measured) is determined from the position where an image of a light spot irradiated at an incident angle of about 60 degree from a first light path 2109 is formed on a first detector. In FIG. 29, 2101 designates a light source, 2106 an object of measurement, 2108 a first photo-detector, 2118 a second photo-detector, and 2119 a second light path.
Also, a conventional apparatus for detecting the inclination of an optical multilayered structure such as a semiconductor wafer detects the inclination and focal point in a manner as described in FIG. 2 showing JP-A-63-146013 providing the first well-known example. In this well-known example, for detection of a focal point, a converged light is irradiated on a wafer, and the position of the light reflected therefrom is formed as an image on a position sensor by an image-forming lens, so that the height (focal point) is detected from that particular position. As to the inclination, on the other hand, it is detected from the position of detecting parallel light rays irradiated on a wafer and converging the reflected light on a position sensor by a convergence lens. In both methods of detection, it is difficult to take an incident angle of 85 degree or more to the wafer, and the resultant great amount of refracted light entering the film coated with resist makes it difficult to detect the true resist surface. For this reason, the position of detection deviates considerably from the position of the true resist surface depending on the reflectance of the base or the resist thickness. It is thus necessary to set an offset value by a trial exposure for each process of wafer exposure.
Also, in a later stage of LSI exposure process, such as the process of exposure of a wiring pattern, for example, the roughness of the wafer surface becomes so great that the photoresist coated thereon becomes rough considerably if not as much as the original wafer surface. If the above-mentioned conventional method is applied to this structure, it would be unknown which portion of the rough photoresist is measured in inclination or height, resulting in a deteriorated accuracy.
The aforementioned prior art fails to take into consideration the fact that the information on the inclination and height in an exposure area is to be accurately obtained with respect to a multilayered structure such as a wafer having a semiconductor circuit pattern, and thus poses a problem in controlling the inclination and height with high accuracy as demanded for the future exposure of a circuit pattern of 0.5 .mu.m or less.